Where can you find high performance intake manifolds, whats the best to get for the LT1, and do you need to change anything when getting a better one?

 

you can port what you have at home. Just minor proting. You can buy a LT4 from GM or ebay, but beware of buying from ebay. Because, anyone can paint the manifold RED.

 

Of course the LT4 manifold won't bolt on the LT1 heads without some machine work to clearance an interference at the valve cover rail.... and after you did the work to bolt it on, you'd find it was really no different than the LT1 intake. The LT4 heads have raised inlet runners, but GM seemed to run out of cash on the LT4 development program, and just copied the LT1 intake, with some extra metal at the top of the runners, so you could enlarge the intake runners to match the head runners, IF you were serious about performance.

The LT1 intake is good enough that Edelbrock spent a couple years trying to improve on it, announced a replacement and even displayed it at trade shows, and then never sold it because it was no better than stock.